Metal cones for cathode ray tubes



Dec. 24, 1957 H. R. SEELEN 2,317,455

METAL CONES FOR CATHODE RAY TUBES Filed Feb. 24, 1951 2 Sheets-Sheet 1 PUMP a9 llllllitl INVENTOR HarJ R. See-Jen ATTORNEY Dec. 24, 1957 H. R. SEELEN METAL CONES FOR CATHODE RAY TUBES 2 Sheets$heet 2 Filed Feb. 24; 1951 INVENTOR 17.2173 B. Seelen United States Patent METAL CONES FOR CATHODE RAY TUBES Harry R. Seelen, Lancaster, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application February 24, 1951, Serial No. 212,546

12 Claims. (Cl. 220-'-2.3)

This invention relates to improvements in cathode ray tubes having composite glass-andmetal envelopes. More particularlyit relates to improvements in metal cones for thebulb portions of such tubes.

Recently, as for example, in the invention described in copending application of Richard. D. Faulkner Serial No. 120,400, now U. S. Patent 2,682,963 filed on Octoher 8, 1949, and assigned to the assignee hereof, certain advances have been made in the cathode ray tube art resulting in the successful commercial production of such tubes with composite metal and glass envelopes. The, bulb portion of any of the presently available composite types usually comprises two parts: a round metal, cone, i. e. one which has circular transverse cross-sections, and a circular glass face-plate'sealed into a rim or lip at the large end of thecone.

These prior art composite structures involve a number of disadvantages. A principle disadvantage is that cabinet space is wasted. This results from the inherent inefliciency of using a round cone and a circular face-plate where the electron beam is to scan through, a rectangular solid angle and to trace a rectangular raster. This Waste of space becomes progressively more serious as screen sizes increase. It makes cabinets needlessly expensive and complicates their design. Another disadvantage is that round tubes are diflicult to mount.

Therefore, it is desirable toprovide rectangulartypes of metal cones and. to make with them cathode ray: tube envelopes with rectangular bulbs and face-plates.

In general, these and other objects. are attained by using in combination two metal-Working operations. of different kinds: (1) spinning thecentralportion of a sheet metal blank over the outside of. a hard-surfaced round frustum; and (2) forcing the partially formed blank by an outwardly acting means to assume the internal shape of a rectangular female die. In spinning the center portion of a flat metal blank suilicient ,pressure should be used to reduce it in thickness while imparting to it :the shape of the frustum. Inthis step the peripheral portion of the blank may be left undisturbed extending in its original full thickness from the spun portion like the brim of a hat. The outwardly actingmeans maybe hydrostatic pressure or a male. punch having the conjugate shape of the die. This combination of steps results .in efilcient use of material since the spinningstep thins out a portion of the blank which eventually forms the part of the cone, its mantle, where theleast strength is needed, while the other step formsthei otherportioninto the rim, the sealing flange and a peripheral portion of the mantle adjacent theretmforming them with sections as thick as the original material and thus providing maximum strength where it is mostneeded. This process also results in an economy of machine operations since most of the needed stretching of the blank is easily effected by the spinning step whereby it is possible to accomplish the rest ina single operation, such. as in one deep draw. The presentinvention minimizes: the loss of .metal as scrap; the required number of machine and machining diagonal.

operations and of annealing steps; and the amount of shrinkage due to cracked and/or otherwise imperfect cones. In addition it results in a cone shape which is highly desirable both for its appearance andstrength and becauseit simplifies a later-required step of settling phosphor material on the inside surface of the faceplate.

In the drawing:

Figure l is a front view into arectangular metal cone, embodying the present invention, as seen through. the face-plate sealing flange;

Figure 2 is an exterior plan view of a cathode ray tube, partially cut away, which comprises a cone as shown in Figure 1 with a face-plate sealed intothe rectangular flange on the front thereof and a neck fusedontoa round flange. at its back;

Figure 3 is an exterior side viewof the tube shown in Figure 1;

Figure 4 shows a developed flat metal blank of an approximately oblately circular or eliptical shape which is preferred in making a cone as in Figures 1 and 2 in accordance with the present invention for reducing to a minimum the amount of trimming of excess material from the front edge of the sealing flange which win be necessary after the second metal-working operation has been completed; and

Figures 5 and 6 show apparatus suitable for re-forming a partly spun blank intoa rectangular cone.

The cone 10 shown in Figures 1, 2,,xand 3 comprises a principal portion herein designated as, the -mantle 11 and two other portions between which the. mantleextends, namely a small round sealing flange 12, at the back of the cone, to which a neck 13 may be fused, and a large rectangular flange 14, at its front, into which the face-plate 15 may be sealed. In Figures 2 and 3 there is shown a point P which represents the center of .defiection of the electron beam.

Unlike a round cone, cone 10 does not have the. same included angle all around, i. e. an angle large enough to provide for the largest amount of deflection. required at any point to scan a rectangular raster with a 3 to 4 aspect ratio. Instead, as examples, three of its included angles having their apices at P are respectivelysubtended by the highest part of the screen, its widestpart, and its These angles are of different sizes, namely 50, 66, and 70, respectively.

Because of this it is diflicult, especially with the rather refractory chrome bearing alloys which are preferred for kinescope cones, to reform a partially spun round blank, e. g. by a drawing or punching operation, without causing excessive stretching in some areas, resulting in splits or cracks, and/or excessive gathering of the incompressible material in others, resulting in folds and pleats. However, according to the present invention, this can be accomplished provided the included angleof the frustum 16 (Figs. 5 and 6) whichis produced by "the spinning operation is appropriately smaller than the largest included angleof the rectangular cone and larger than its smallest included angle, e. g., if it is 60 for the cone shown in Figures 1-3. If this is so, then in the reforming operation the slack developed, by pushing the top and bottom nearer together can be taken up by the pulling of the sides apart.

At the present state of the art certain chromium bearing alloys are the preferred materials for kinescope cones, even though they are more diflicult to work and more expensive than other materials such as cold rolled steel. One reason for which they are preferred is that their expansion-contraction characteristics are appropriately related to those of suitable types of glass forfg encrating certain usefulcompressive forces, therein, during the manufacturing process, and for not generating certain harmful tensile forces. For example, useful con c mum heights, widths, etc.

pressive forces are produced in the face-plate by shrinkage of the sealing flange around it after sealing-in. This causes the face-plate to bulge outward improving its ability to oppose the inwardly acting force of atmospheric pressure which becomes effective upon evacuation. Another reason is that the chromium in these alloys produces an oxide film on the sealing flanges when they are heated for sealing-in, and, due to the solubility of chromium oxide in molten glass, this strengthens the seals. However, this elementnot only is an expensive ingredient in these alloys but also makes them difiicult and expensive to roll into sheet material and to work into finished articles. As a result the cone is usually the principal item in the over-all cost of glassand-metal picture tubes, particularly those having large screens since their cones may easily weigh 12 to 15 pounds. Obviously, therefore, in these tubes it is very important to avoid using more cone material than is really necessary. The problem was met for the manufacture of round cones first by the use of high pressure spinning. As is well known the effect of high pressure spinning over a round conical mandrel is to thin out the material, by an amount which is a function of the sine of the included angle, thereby effectively causing a given weight of material to extend over a larger portion of the area of the cone than if it were fabricated in some other way such as by drawing. In general, the blank material must be thick enough so that the face-plate sealing flange as formed without thinning will be strong enough. Because of this, and since the amount of thinning obtainable in the mantle is limited, many cones, even though they were spun under high pressure have had thicker side walls then necessary and therefore have been somewhat wasteful of material. However, further economy was made possible, as taught in the abovementioned copending application, Serial No. 120,400, by an improved structural design which permits fabrication of the cone from a thinner blank than formerly. In a cone of this design the walls of the mantle as formed of the thinner blank and as further thinned by spinning are no longer too heavy and yet the sealing flange is sufficiently strong because it is reinforced by an adjacent portion of the mantle which is spun at a sufficiently reduced pressure to be approximately as thick as the flange.

According to the present invention it is possible to make a rectangular cone so as to attain the advantages both of sine law spinning and of the feature set forth in the above-mentioned copending application.

An apparatus used to practice the presently disclosed method of making rectangular cones comprises a rotatable frustum of hard-surfaced material, onto the small end of which a flat blank may be attached and keyed so as to be rotated therewith, and one or more rollers for progressively urging successive portions of the blank under very great pressure against the outside surface of the frustum starting near its small end and progressively advancing down the side thereof toward its base to force material ahead of it and to spin it into the shape of the frustum. According to the present invention such apparatus is not utilized for processing as much of the flat blank as in forming a round metal cone. Instead only a center portion of the blank is spun to form thereof a hollow frustum 16 (Figs. and 6) of a depth which is 'smaller than, and preferably bears a predetermined relationship, to the desired depth for the finished rectangular cone. Among different specific cones this relationship will vary as a function of differences in a number of their parameters such as the aspect ratios of their face-plates, their respective included angles, their maxi- However, for a cone proportioned as in Figures 1-3 the preferred ratio of the depth .of the spun frustum 16 to that of the complete cone, 10, is of the order of 7 to 8%.

Apparatus for the spinning operation of the present invention is not shown herein since a number of suitable kinds are already known. However, two kinds of apparatus for performing the other operation are shown in Figures 5 and 6 respectively. The manner in which they are used is explained below.

The oblately circular or elliptical blank 17 is cut from sheet metal stock so that the grain thereof, as represented by an arrow in Figure 4, extends in the direction of its minor axis. This is done because the second metal working operation can be accomplished with more uniform results and less shrinkage losses if the partially formed blank 20 is so oriented with respect to the female die that a line corresponding to the original grain of the stock extends crosswise to the large open end of the die rather than lengthwise thereto. A round hole 18 is provided at the center of blank 10, i. e. at the intersection of its major and minor axes. This hole is intended to fit snugly over a short cylindrical arbor which protrudes from the small end from the hard surfaced frustum used in the spinning operation and which, as shown in the abovementioned copending application, may be threaded to provide a means for clamping the blank onto the frustum. Two other holes, 19, are provided for engaging off-center pins which may also protrude from the small end of the frustum, which serve for keying the blank thereto so that they will rotate together. A small hole, 22, or a row thereof, may be provided to indicate the direction of the grain. Since the blank is very nearly round, this will be helpful for an operator and will tend to shorten the time he will require to properly orient a partially formed blank 20 in the stamping mill. In the stamping mill represented in Fig. 5, a female die 21 is mounted on the bottom, free end of an hydraulically actuated piston 24 with its hollow interior directed downward. A male punch 25 is rigidly supported on a base 26 so that it points upward with its axis coinciding with that of the piston 24.

Before reforming the blank 20 on the stamping mill, it is preferable to anneal it and to provide it with a surface lubricant or drawing compound. Satisfactory annealing of a partially formed blank of inch stock has been accomplished in 6 minutes at 1650 degrees Fahrenheit. This sufliciently eliminates a tempering effect which is incurred in the spinning operation. Water soluble soap types of lubricant are quite suitable and have the advantage that they are readily removable from the finished product by washing it in water.

After the partially-formed blank, 20, has been annealed and dipped in lubricant it is placed on the punch 25 as shown in Fig. 5 and then the female die is brought down upon it with a sufficient pressure to reform it in a single draw.

It has been found that a 500 ton impact or mechanical type of stamping mill is adequate for reforming a partially-formed blank, 20, which has a maximum wall thickness of .1 inch at the flange and consists of 17 percent chromium bearing iron alloy, into a rectangular cone whose sealing flange has a 17 inch diagonal. However, if an hydraulic stamping mill is used, it should be heavier. Moreover, whatever the type of mill, faster and more satisfactory results will be obtained if its capacity substantially exceeds the permissible minimum. If desired the male punch 25 may include as a protrusion from the center of its top surface, a short cylindrical cutter 27 which in cooperation with a sharp-edged cylindrical socket 28 correspondingly located in the female die may serve for piercing the neck opening 23. This opening, which corresponds to the area enclosed in a dotted circle in Fig. 4, is about 5 /2 inches in diameter in the 17 inch diagonal cone mentioned above. However, the preferable way of practicing the present invention is to pierce the center hole in a separate operation following the reforming one. The reason for this is that if the piercing of this hole is accomplished as part of Moreover, the partially-formed blank will be somewhat less free to shift about so as to accommodate itself to the progressively lesseningspace between the punch and die during reforming if any part thereof becomes captive too early in the operation as may be the case where the piercing operation is combined with reforming.

In order most successfully to form a rectangular cone without cracks and/or pleats and with smooth contours as shown in Figures 1-3, the following are some of the precautions which should be taken: the included angle of the spun frustum 16 should bear the proper relationship to certain reference included-angles for the desired rectangular cone; the depth of the frustum 16 should bear [the appropriate ratio to the depth of the desired finished cone; and the die and punch should be shaped toimpart to the top, bottom, and side panels of the rectangular.

cone a degree of convexity whereby they will constitute outwardly curved panels.

The last of these precautions offers several advantages: it helps to take up slack, gathering, which tends to develop in the reforming operation; it results in .a geometrical shape which affords great side wall strength towithstand atmospheric pressure and to minimize flange distortions and seal ruptures as a result thereof; and it provides a bulb shape, for the finished envelope, which does not complicate the operation of applying afluorescent screen to the face plate by a corner-settling probformation of small irregularities on its inside sealing surface, i. e., such as small wrinkles and folds. For this reason it is advantageous to perform a coining operation for reforming the large sealing flange. The

punch and die employed for coining may be very much like those shown in Figure 5 with appropriate portions of their surfaces cut back to clear the cone in the region of its mantle and small sealing flange. As a result the full pressure of the stamping mill will be brought to bear on the large sealing flange to provide the very high pressure per unit area needed for coining. After coining the drawing compound may be washed off with water.

While it may seem desirable to anneal the cone after the reforming operation in order to relax strains built up in that operation, this has the disadvantage that it may affect the shape of the cone. However, where such a second annealing is used, if it is followed by the coining operation, the flange will be at least partly restored to the desired shape.

By using a blank 17 having the shape shown in Fig. 4 and by properly orienting it in the stamping mill, there will be very little fringe protruding from the lip, or rim, 29 of the face-plate sealing flange after the cone has been processed to the point thus far described. However, the small amount of fringe which does protrude should be removed. Since the amount which needs to be trimmed is small, it is possible to remove it by burring and/or finish-grinding. However, it has been found to be preferable to saw it from the lip on a high speed metal band saw. In doing this, it is advantageous to mount the rectangular cone in a fixture permitting the entire cone to be rotated about an axis corresponding to that of the neck 13 whereby to progressively feed the lip into the saw blade at the point where it passes through the band-saw table. This axis of the fixture should be angularly movable in a vertical plane about a pivot which. is spaced back from the intersection of the saw blade and the table by a distance substantially equal to the radius of curvature of the .undulant edge shown in Figs. 2 and 3.

abrasive.

Fig. 6 shows an. alternative apparatus for the operation of reforming the partially formedblank 20. It comprises a die 30 which has the same interior configuration as the die 21 but which, as shown, is employed with its large opening facing upward. A plug 31 is used for closing the holes 18, 19,..and 22. The plug comprises a somewhat mushroom-shaped'bolt 32, a rubber gasket 33, a heavy washer34, and a nut 35. Thehead of the bolt 32 may be shaped as shown to guide the direction of expansion of frustum 16 into the die. The apparatus of Fig. 6 also comprises aheavy cover 36 carrying a rubber sealing ring 37 fitted into an ovately circular groove 38 in its lower surface. To reform the blank 20 the plug'31 is'attached to it; it is placed in the die 30 as shown; and the cover 36 is forced heavily down against it whereby the. space inside of the frustum 16 is entirely sealed. Then liquid, such as thick oil, is forced underextremely high pressure. from a pump 39, thru .a

passageway 40, and into the frustum 16 to force it to expand outwardly until itfills the die 30.

As is most clearly shown. in Figs. 2 and 3 one result of producing a rectangular cone according to the present inventionis that a portion, 41, of the mantle 11 adjacent the face-plate sealing flange 14 is formed without thinning, i. e., it is as thick as the original fiat blank 17. According to the teachings of the above-mentioned copending application this structural feature lends such support to the sealing flange that in making the cone it is possible to start out with thinner material than would otherwise be possible and therefore wastage of metal in the mantle can be avoided.

Since every point of the perimeter of the sealing surface of the flange 14 is equidistant from a point correthe shape of a frustum. That is to say, while the working surface must be a figure of revolution, the slope of the sides does not have to be along a straight line but instead maybe along a line which curves either inward or outward with respect to the axis of rotation. Moreover, theslope of the sides may be straight for part of the way and then curved. For example, the sides may slope downward along a straight line in the fashion of a true frustum and then curve outward so that it merges gradually into the rim portion of the hat-like partially formed blank.

While the face-plate sealing flange presents an undulant profile as the cone is viewed laterally, .it is within thescope of the present invention to form the flange with a flat edge. A cone with such a flange if laid on a flat surface with its large opening facing downward would rest uniformly on the surface all the way around .the flange. Obviously, if the cone is to be made this way, the die used for reforming a partially formed blank would have to be modified accordingly and this would also be true for a die and punch used for coining. While a flatface-plate can be used with such a cone if it is made thick enough to have the requisite strength, it is pref} erable to provide the needed strength byforming the plate to be outwardly curved. Such a plate can be made .by supporting a flat glass blank on a flat rectangular frame by its edges only and heating it until the center of the blank sags down within the frame. Of course, such a plate is turned over before it is placed in the cone sealing flange preparatory to sealing in.

Another possibility is to form the cone with outwardly undulant profiles for the two short sides of its faceplate sealing-flange and straight profiles for the two long sides thereof. In this case the face-plate has the shape of a rectangular section cut out of a cylinder of glass rather than out of a sphere. This form has the advantage that almost all of any ambient room light which may fall on the outside surface of the television picture tube face-plate will be reflected either upward or downward and hence out of the field of vision.

What is claimed is:

1. A television tube body of substantially frusto-pyramidal form; a substantially circular opening at the smaller end; a substantially rectangular opening at the larger end; a substantially rectangular seating ledge for receiving a spherically curved viewing screen at said rectangular opening; the four sides of the inner boundary of said seating ledge lying on the intersection of a sphere with said frusto-pyramidal body, the center of the sphere and the generating point of a conical surface which includes the smaller circular opening and which intersects at least two opposite boundaries of the rectangular opening both lying along the axis of the tube body with the generating point of said conical surface lying between the center of the sphere and the smaller end of the tube body.

2. A television tube body of substantially frusto-pyramidal form; a substantially circular opening at the smaller end; a substantially rectangular opening at the larger end; a substantially rectangular seating ledge for receiving a spherically curved viewing screen at said rectangular opening; the four sides of the inner boundary of said seating ledge lying on the intersection of a sphere with said frusto-pyramidal body, the center of said sphere and the generating point of a conical surface which includes the smaller circular opening and which intersects at least two opposite boundaries of the rectangular opening both lying along the axis of the tube body with the generating point of said conical surface lying between the center of the sphere and the smaller end of the tube body; retaining lip extending beyond said seating ledge.

3. A television tube body of substantially frusto-pyramidal form; a substantially circular opening at the smaller end; a substantially rectangular opening at the larger end; a substantially rectangular seating ledge for receiving a spherically curved viewing screen at said rectangular opening; the four sides of the inner boundary of said seating ledge lying on the intersection of a sphere with said frusto-pyramidal body, the center of said sphere and the generating point of a conical surface which includes the smaller circular opening and which intersects at least two opposite boundaries of the rectangular opening both lying along the axis of the tube body with the generating point of said conical surface lying between the center of the sphere and the smaller end of the tube body; a retaining lip extending beyond said seating ledge, and a reinforcing band between said seating ledge and the body of the tube.

4. A metallic television tube body of substantially frusto-pyrarnidal form; a substantially circular opening at the smaller end; a substantially rectangular opening at the larger end; a substantially rectangular seating ledge for receiving a spherically curved viewing screen at said rectangular opening; the four sides of the inner boundary of said seating ledge lying on the intersection of a sphere with said frusto-pyrarnidal body, the center of said sphere and the generating point of a conical surface which includes the smaller circular opening and which intersects at least two opposite boundaries of the rectangular opening both lying along the axis of the tube body with the generating point of said conical surface lying between the center'of the sphere and the smaller end of the tube body; a retaining lip extending beyond said seating ledge, and a reinforcing band between said seating ledge and the body of the tube; said seating ledge, retaining lip and reinforcing band being substantially of equal regular thickness and being substantially thicker than the main wall of the tube body.

5. A tclevisiontube body of substantially frusto-py ramidal form; a substantially circular opening at the smaller end; a substantially rectangular opening at the larger end; a substantially rectangular seating ledge for receiving a spherically curved viewing screen at said rectangular opening; the four sides of the inner boundary of said seating ledge lying on the intersection of a sphere with said frusto-pyramidal body, the center of said sphere and the generating point of a conical surface which includes the smaller circular opening and which intersects at least two opposite boundaries of the rectangular opening both lying along the axis of the tube body with the generating point of said conical surface lying between the center of the sphere and the smaller end of the tube body; a retaining lip extending beyond said seating ledge, and a reinforcing hand between said seating ledge and the body of the tube; said seating ledge, retaining lip and reinforcingband being substantially of equal regular thickness and being substantially thicker than the main wall of the tube body, and a supporting ledge at the boundary of said circular opening; said last-mentioned supporting ledge having a thickness substantially equal to that of the seating ledge at the first-mentioned portion of the tube body.

6. A television tube body of substantially frustopyramidal form; a substantially circular opening at the smaller end; a substantially rectangular opening at the larger end; a substantially rectangular seating ledge .for receiving a spherically curved viewing screen at said rectangular opening; the four sides of the inner boundary of said seating ledge lying on the intersection of a sphere with said frusto-pyramidal body, the center of the sphere lying along the axis of the tube body, said tube axis being substantially normal to the plane of said circular opening at the center thereof.

7. A metal shell for ardischarge tube, said shell comprising a plurality of walls joined to form a hollow substantially frusto-pyramidal body, said body having a large opening at one end thereof, said shell including a sealing surface at said opening, said sealing surface being determined by the intersection of said walls with a spherical surface.

8. A metal shell comprising a plurality of walls joined to form a hollow substantially frusto-pyramidal body, said body having a large opening at one end thereof, said shell including a sealing surface at said opening, said sealing surface being determined substantially by the intersection of said walls with a spherical surface, and a spherical glass plate sealed to said sealing surface. I

9. A metal shell for a discharge tube, said shell comprising a plurality of walls joined to form a hollow substantially frusto-pyrarnidal body, said body having a large opening at one end thereof, said shell including a sealing surface at said opening, said sealing surface being determined substantially by the intersection of said walls with a spherical surface, and a spherical glass plate sealed around its periphery to said sealing surface, said glass plate conforming substantially with said spherical surface.

10. A shell for a cathode ray tube, said shell comprising a plurality of metal walls joined together to form a substantially frusto-pyramidal body, said body having a large opening at one end and a small opening at the opposite end thereof, said openings each having a center positioned on a common axis, said body having at said large opening a sealing surface determined by the inter:

section of said metal walls with a spherical surface center of curvature is on said axis.

11. An envelope for a cathode ray tube, said envelope comprising a plurality of metal Walls joined together to form a substantially frusto-pyramidal body, said body having a large opening at one end and a small opening at the opposite end thereof, said openings each having a center positioned on a common axis, said body having at said large opening a sealing surface determined by the intersection of said metal Walls with a spherical surface whose center of curvature is on the portion of said common axis extending through the other of said openings, and a spherical glass plate sealed at its periphery to said sealing surface.

12. An envelope for a cathode ray tube, said envelope comprising a plurality of metal walls joined together to form a substantially frusto-pyramidal body, said body having an opening at each end thereof, said openings each having a center positioned on a common axis, said body having at one of said openings a sealing surface whose 10 determined substantially by the intersection of said metal walls with a spherical surface whose center of curvature is on the portion of said common axis extending through the other of said openings, a spherical glass plate substantially conforming to said spherical surface sealed around its periphery to said sealing surface, and a tubular glass element sealed to said body at the other of said openings.

References Cited in the file of this patent UNITED STATES PATENTS 2,035,408 Rothschmitt Mar. 24, 1936 2,219,574 Fraenckel Oct. 29, 1940 2,232,098 Deichman Feb. 18, 1941 2,236,708 Grimditch Apr. 1, 1941 2,254,090 Power Aug. 26, 1941 2,517,584 Mapes Aug. 8, 1950 2,682,963 Faulkner July 6, 1954 2,782,953 Koch et al Feb. 26, 1957 

